Until recently, it was widely believed that gas bubbles inside magma only form when pressure decreases during its ascent toward the surface, much like when opening a bottle of soda. Scientists have long wondered why some volcanoes erupt violently, while others flow smoothly, even though the magma in both cases contains the same amount of gas. In an attempt to answer this, a recent study by researchers from ETH Zurich revealed that the crucial factor is the shear forces within the magma (the forces that act on a body in a way that makes its parts move in opposite directions, like the process of kneading). Under the high pressure deep within the volcano, the gases remain dissolved.
